It is now well known to use acquired data for generating images on a video screen within imaging systems. Such generated images are used in fields as diverse as astronomy, aerial surveying, aerial surveillance, and medical diagnostics. An advantage of generating images from acquired data is that it is much easier to process the data to enhance such images than when photographs are taken directly or when video cameras are used to directly project the images onto a TV screen.
Imaging systems using acquired data generally are comprised of four major sections. First, there is the data acquisition section. For example, in digital fluorography, the acquisition section of the system comprises an X-Ray tube, the detector and an image intensifier along with a video camera for converting the intensified, detected image to electrical signals.
Following the acquisition section of the system is an image processing section, where a good deal of the enhancement is accomplished and which directs the electrical signals to an image memory where they are stored on an element by element basis that corresponds or can be made to correspond to the pixel designation of the actual displayed image. The image processing section also includes a timing generator for generating the timing signals required for displaying the data as an enhanced video image.
In addition to the image processor section, there is the multi-processor section which is the main control section and includes central memory means and the main processor sub-sections. Finally, there is the display section where the processed data generated image is displayed.
In general, when utilizing video signals and displays, an attempt is made to lock the system's generated signals to the power line frequency signals. It is desirable to line lock image processing systems in order to stabilize the image display, to avoid frequency jitter and to reduce the adverse effect of hum noises.
Another reason for the line locking is applicable when the imaging system acquires data using X-Ray equipment. When the X-Ray tubes are operated on a pulse basis, they are generally locked to the line. For a general synchronization of the system, it is extremely desirable to line lock image processing systems, especially when the acquisition portion operates with X-Ray equipment.
There are, in general, two different power line frequencies used in the world. In the United States, for example, 60 Hertz frequency is standard; whereas, in Europe and the Middle Eastern countries, 50 Hertz is standard. This duality of line frequencies raises problems because modern day manufacturers manufacture for the world at large. Thus, the manufacturers of image processing equipment have to take into accound this distinction in line frequencies. The imaging processing equipment, as presently available, is designed to lock into either a 50 Hz frequency or a 60 Hz frequency. When equipment is designed to lock in at the 50 HZ frequency, then the basic frequency of the processing system is some product of 50 HZ per second; whereas, when the system is designed to lock in at the 60 HZ frequency, then the basic frequency of the system is some product of 60 HZ.
There is a distinct advantage to having the system operate at the basic 50 Hz rate. When the system is operating at a basic 50 Hz rate then the basic time unit of the system is 20 milliseconds, when the system is operating at a basic 60 Hz rate, then the basic time unit is 16.6 milliseconds. Thus, with the 50 Hz system, if all other things are equal, there is more time for the software or dedicated hardware systems to operate and fulfill their functions. The difference of 3.4 milliseconds seems small at first, but that time period has to be viewed in the proper perspective. When operations occur in the nanosecond range, 3.4 milliseconds is a long time. For example, standard 50 Hz systems display a full 512.times.512 matrix and use the additional lines for alphanumeric information.
Accordingly, it is an object of the present invention to provide image processing systems, that operate at a basic low frequency rate, regardless of whether the line frequency is 50 Hz or 60 Hz.